In 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, specifications are being designed to enhance LTE (Long Term Evolution) in order to comply with the rapidly increasing traffic demands (for example, see 3GPP Technical Specification “TS 36.300 V12.0.0” January, 2014).
At the same time, a specific frequency band available without a license (Unlicensed Band/Unlicensed Spectrum) has attracted attention. As a means for responding to a rapidly increasing traffic demand in a mobile communication system, it may be possible to utilize the above-described specific frequency band for the mobile communication.